Gas-to-liquid mass transfer has numerous industrial applications. Soluble gases, such as carbon dioxide and ammonia, can be captured and absorbed into a solvent such as water. One particular application where gas-to-liquid mass transfer has potential for significant growth is in the use of natural sinks for sequestering carbon dioxide or other gases from air. Other applications of gas to liquid mass transfer include the production of microalgae as a feedstock for the mitigation of carbon dioxide emission, and the production of biofuels. Such applications require a consistent and controlled supply of inorganic carbon to the microalgae (or cyanobacteria) culture. The carbon dioxide must be introduced into the growth medium (i.e., water) of the microalgae in a way that does not abruptly and significantly reduce the pH of the growth medium, which may happen as carbonic acid forms when carbon dioxide is absorbed by, and reacts with water.
There are two rate-limiting steps in the transfer of carbon dioxide to water—the gas exchange to the boundary layer in the water and the conversion of the dissolved carbon dioxide into carbonic acid in the water. Carbon dioxide from the air, or any gas containing carbon dioxide, must first transfer into the water (or any liquid which acts as a solvent for carbon dioxide) across a resistive “layer” often called the boundary layer. For ponds or raceways, the boundary layer has an average thickness of several millimeters. Because the rate of diffusion of carbon dioxide into the water is roughly proportional to the thickness of the boundary layer, a thinner boundary layer means that carbon dioxide is transferred into the solution faster. Once in solution, the amount of aqueous phase carbon dioxide begins to build up. The aqueous phase carbon dioxide reacts with the water to form carbonic acid (H2CO3). Because this conversion rate is relatively slow, this conversion is a significant rate limiting step in the process of building up a supply of inorganic carbon (IOC) within a supply of water or liquid, such as in a raceway or pond. There is therefore a need to address these and other issues in the art.